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REXIS Detector Packaging and Assembly

REXIS Detector Packaging and Assembly. Harrison Bralower REXIS Engineering Peer Review 9/18/12. Review Team. Rick Foster (MKI) Steve Graham (GSFC IRT) Don Jennings (GSFC) Steve Kissel (MKI) Bob Reich (LL) Joe Schepis (GSFC) Joel Villaseñor (MKI) Keith Warner (LL). Review Goals.

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REXIS Detector Packaging and Assembly

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  1. REXIS Detector Packaging and Assembly Harrison Bralower REXIS Engineering Peer Review 9/18/12

  2. Review Team • Rick Foster (MKI) • Steve Graham (GSFC IRT) • Don Jennings (GSFC) • Steve Kissel(MKI) • Bob Reich (LL) • Joe Schepis (GSFC) • Joel Villaseñor (MKI) • Keith Warner (LL)

  3. Review Goals • To determine if an appropriate CCD packaging geometry has been designed • To determine if appropriate materials for the CCD package have been chosen for REXIS • To determine if an appropriate detector assembly geometry has been designed that meets instrument alignment and telemetry requirements • To determine if a suitable flexprint cable has been designed that meets the electrical and mechanical needs of the instrument

  4. Review Process • Feel free to ask questions at any time • Please fill out RFA forms for any actions you’d like me or the REXIS team to take • All RFAs will be closed by PDR at the end of January • Paper RFAs should be given to me or Becky • Electronic RFAs should be emailed to me (bralower@mit.edu) and Becky (becki@mit.edu) • We are hoping for a team report of this review (and all other peer reviews) to be issued at some point

  5. Agenda • Project and Instrument Overview • CCD Thermal Environment • CCD Packaging Geometry • Detector Assembly Geometry • Material Selection for Packaging and Detector Assembly • Fe-55 Check Source Design • Radiation Damage Mitigation • Flexprint Cable Design • Scheduling and Cost

  6. Project and Instrument Overview

  7. What is OSIRIS-REx? • The Origins, Spectral Interpretation, Resource Identification, (and) Security REgolith eXplorer is a NASA New Frontiers mission to asteroid 1999 RQ36 • Asteroid has a heliocentric orbit that intersects Earth’s orbit; it can usually be found between here and Mars • 1-in-1000 chance asteroid hits Earth in 2169 • OSIRIS-REx Mission objectives • Return at least 60g of asteroid regolith to Earth and characterize the sample in situ • Globally map the asteroid topology and mineralogy • Measure orbital perturbations due to Yarkovsky effect • Compare data to ground measurements of other nearby asteroids • REXIS is a Class-D student payload whose primary operations occur in Phase 5B of the OSIRIS-REx mission Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  8. What is REXIS? Detector Assembly Support Structure (DASS) Coded Mask • REgolith • We study asteroid dust • X-ray • We monitor X-rays fluoresced out of the asteroid by incident solar X-rays (which we also monitor) • Imaging • We use CCDs and coded-mask imaging algorithms to globally and spatially map the asteroid • Spectrometer • We identify spectral lines in the collected X-rays to determine the chemical composition of the asteroid Radiation Cover Detector Array Radiator Electronics Box Thermal Isolation Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  9. REXIS Science Mission Sun • We want to identify the distribution of elements on the surface of RQ36 with a spatial resolution of 50m or better • O, Mg, Fe, Al, Si, S with SNR > 10 • These all emit X-rays between 0.5-10keV, which the REXIS CCDs can detect with high quantum efficiency and spectral resolution • REXIS supports OSIRIS-REx by finding possible TAGSAM sites of interest • REXIS characterizes candidate sample sites and provides context for the sample return • Monitoring solar X-rays provides context for X-rays measured off the asteroid RQ36 Solar X-rays X-ray Fluorescence (XRF) Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  10. Coded-Mask Imaging • Consider a mask pattern in front of the detectors • Photons from any direction cast a shifted shadow of the mask pattern onto the detectors • Intensity of shifted pattern corresponds to how bright that direction is in the field of view • Simple ray-tracing algorithms can determine what all possible shifted patterns look like • Spatial cross-correlation of data and mask pattern reveals the most statistically likely direction of incident X-rays Detector Plane Image Coded Aperture Mask Reconstructed Image

  11. CCD Thermal Environment

  12. CCD Thermal Environment Asteroid QIR & QAlbedo QSolar QRadiation Sun Radiator Sun Shield Heat Strap (DASS to Radiator) QPower QParasitic EB CCDs OSIRIS-REx S/C Deck Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  13. Thermal Design Considerations • Each CCD must dissipate ~61mW of heat (TBR) • Asteroid IR and albedo, intra-instrument radiative exchange, power to operate the CCDs, and parasitic conduction from electronics • Science requirements demand CCDs remain at -50°C (TBR) or colder • Actual requirement determined by imaging simulation • Baseline CCD design temperature is -60°C • CCDs are passively cooled via conduction through DASS and thermal strap to radiator, which radiates to deep space • Based on simulation the radiator may reach -70°C, leaving 10°C forconduction losses, unmodeled contact resistances, and margin • Lowest achievable radiator temperature in phase 5B is TBR

  14. CCD Packaging Geometry

  15. Lincoln Labs CCID-41 • Heritage dating to ACIS (CCID-17) and Astro-E2 (CCID-41) • Designed for X-ray applications • 1024 x 1026 pixels • 24µm x 24µm pixel size • Consistent with L3 specs • Split frame-store • Back-illuminated • Covered with 220nm aluminum for optical blocking • Supports charge injection • REXIS uses a 2 x 2 array of these CCDs Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  16. CCD Packaging Options • Lincoln can provide different packaging options depending on the application • Invar pedestal • Used for tight-tolerance applications • Invar can be heat-treated to match the CTE of silicon • Kovar/alumina ZIF socket • Used primarily for development applications in a lab setting • Ceramic package • Used for looser-tolerance applications • Cheapest and easiest to produce • Custom packaging(e.g. integrating mechanical and electrical interfaces in one structure for PanSTARRS) Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  17. REXIS Packaging Design • What does REXIS need in a detector package? • Low mass • Good CTE match to silicon • Easy alignment • Replaceable CCDs • Low thermal resistance • Launch survivability • ACIS heritage package meets most of these requirements Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  18. REXIS Packaging Trade • Invar package is not ideal for this application • Coded-mask imaging is very robust against misalignment and other error sources • Invar is heavy and has poor thermal conductivity • Kovar/alumina ZIF package isn’t really intended for flight • Kovar is heavy • Would require custom ZIF socket or other connector • Thermal management would be difficult • CCDs not replaceable • Package not rated below -40°C; REXIS operates at -60°C • CCDs already ship in alignment • Ceramic package is (relatively) simple • Low mass (4 packaged ACIS CCDs have a total mass of ~200g) • Easy to connect to electronics since we pick the connectors • CCDs are individually replaceable • Thermal management much simpler • Rated to -80°C (according to LL); has flown at -120°C (ACIS) • Harder to align—each CCD must be in alignment individually

  19. REXIS Packaging Design CCD (underlying adhesive not shown) • Design is almost the same as ACIS package • Some design elements subjected to trades or redesign • Ceramic substrate material • Metal parts material • Flexprint design Ceramic Substrate Metal Tee Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  20. Detector Assembly Geometry

  21. Detector Assembly Requirements • What do we need in a detector assembly? • Low mass • Low thermal resistance • Keep CCDs aligned with respect to each other and the mask • Protect CCDs from radiation damage • Shield frame-store from incident photons • Minimize stray light from striking CCDs • Provide means of checking CCD degradation in flight • Fit within existing REXIS footprint (if possible) • Provide breakout of CCD electrical connections to electronics • Must not fluoresce in detectable range • All aluminum parts in field of view will be gold-coated

  22. Detector Assembly Requirements • Distance between active imaging areas of CCDs 768 ± TBR µm • REXIS bins single 24µm x 24µm pixels into 16 x 16 (384µm x 384µm) superpixels • Gaps in data should be an integer multiple of superpixel size • Actual gap between packages is less due to inactive silicon on die edges • Tolerance on requirement is TBR by HCO • Maximum misalignment requirements • ΔX/ΔY translational shift (in detector plane): ±0.0384cm • ΔZ translational shift (normal to detector plane): +6.67/-4.00cm • Rotational shift about X and Y: ±1.54° • Rotational shift about Z: ±0.40° • All mechanical parts must have first natural frequency >90Hz (TBR) • All mechanical parts must survive launch • Will perform preliminary launch load and vibration analysis before PDR

  23. REXIS Detector Assembly Mount (DAM) Flexprint Attachment Points Fe-55 Source RTV Pocket Package Carrier Tee (bondedto package) Delivery Box Mount Point Active Imaging Area Assembly Tension Screw Flexprint Slot Radiation Shield Alignment Pin Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  24. REXIS Detector Assembly Mount (DAM) Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  25. REXIS Detector Assembly Mount (DAM) • DAM Mass and Size • 329.83g • 11.39cm(L) x 8.16cm(W) x 2.87cm(H) • Does not include flexprint or radiation cover Flexprint Route Flexprint Bonded to Package Here Connector Oriented Normal to End Shield Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  26. Material Selection for Packaging and Detector Assembly

  27. Thermal Model of Assembly Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  28. Ceramic Substrate Trade • Two metrics: CTE match to silicon and thermal conductivity • Cost not a metric due to low price per part and low part volume • Substrate thickness still an open trade • Nominally 1/8” from ACIS heritage • Need to do shock/vibration analysis to find minimum substrate thickness Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  29. Ceramic Substrate Trade

  30. Metal Parts Trade • Detector assembly has three metal parts (not including radiation shielding) • Tee (bonded to package) • Array structure (holds CCDs and is screwed into the DASS) • Package carrier (screwed into array structure and bonded to CCD package with RTV epoxy) • Considered two materials: Beryllium and aluminum • Plot on previous slide includes only aluminum parts in model • ΔT across DAM lower than expected with aluminum parts • Beryllium provides lower mass, higher thermal conductivity, and better CTE match to other parts at significant risk to project • No justification for using beryllium in design

  31. Fe-55 Check Source Design

  32. Fe-55 Check Source • CCDs degrade with exposure to space environment • Spectral lines shift in mean energy and become broader with time • Installing a known radiation source in the assembly can be used for in-flight calibration and monitoring of CCD health • Fe-55 is a very common laboratory radiation source • Fe-55 has peaks at 5.9keV and 6.4keV, which can be used to check CCD performance against requirements set at 6keV • Requirements for check source • Must not radiate towards other instruments on OSIRIS-REx • Must provide enough counts • Must not contaminate asteroid data • Proposed source: Eckert & Ziegler IERB19058 • 81nCi ± 30% activity; 50mm(L) x 2mm(W) x 0.3mm(H)

  33. Fe-55 Source Placement • Source placement driven by data constraints • Not enough data allocation to illuminate whole array • Even at 100 counts per second (cps) source activity we only get 22 counts per hour per superpixel for illuminating the whole array • This is not enough telemetry data but would be half of the overall data budget • Since we are primarily interested in how each CCD varies along the readout direction we can illuminate a one superpixel-wide strip along the edge of each CCD • At 10cps activity we get ~200 counts per hour per superpixel, which is equivalent to ~5% of the overall data budget • This assumes the CCD does not spatially vary perpendicular to the readout direction

  34. Fe-55 Source Placement Radiation Shield Collimator Abutment Gap Fe-55 Source Pockets for Mass and Thermal Resistance Reduction Shim Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  35. Radiation Damage Mitigation

  36. Radiation Cover Hinge Frangibolt Aluminum Cover Weak Point Titanium Bolt Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  37. Radiation Damage • Electronics require shielding from ionizing and non-ionizing radiation • Most chips will latch up or fail • REXIS does not use latching chips • CCDs degrade instead • Non-ionizing radiation will displace silicon atoms from crystal lattice and create electron traps • Decreases charge transfer efficiency (CTE) in CCDs, which shows up as a gain decrease • To first order, CCDs will record sum of actual and gain-shifted peaks • As gain shift increases with damage, spectral lines get broader Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  38. Radiation Damage • Spectral lines widen until science requirements are violated • Charge injection will delay this • Data from Astro-E2 relates change in CTE to radiation dose for REXIS CCDs • By finding lowest tolerable CTE we can find the maximum acceptable dose and size the shield • Current depth: 5.5mm (TBR) Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  39. Flexprint Cable Design

  40. Flexprint Cable Requirements • Low mass • High thermal resistance • Circuit remains out of CCD FoV • Mounts to detector assembly • Must survive launch • Must provide strain relief on flexprint • No vias on CCD end • Kavli has shown via failure under thermal cycling • Shielded video output/frame-store lines • Glenair 890-011 37-pin Nanominiature connector is current baseline • .725”(L) x .125” (W) x .255”(D) • Looking into AirBorn connectors for compatibility with existing detector electronics Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  41. Flexprint Cable Design • This circuit delivers analog video through output JFETs to the detector electronics • Also contains reverse-protection diodes and filter capacitors, plus an RTD for monitoring CCD temperature • Four layers at rigid connector end, one layer in flexible middle and rigid CCD end • Smaller and more compact than Astro-E2 flexprint • Output connects to electronics box via jumper cable • Routed either through DASS or out truss side panels—trade still open 4-Wire RTD 2-56 Through Holes Output Protection Diodes Connector Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  42. Flexprint Cable Design Strain Relief Zones • Frame-store and output video lines are shielded at entry to the rigid connector end • Does not appear in Gerber files • Mechanical design of flexprint has 1.1mm bend radius for strain reliefs at CCD end and in the middle • Is this enough strain relief? Shielded Zone Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  43. Scheduling and Cost

  44. Engineering Model Scheduling Regolith X-ray Imaging Spectrometer – REXIS – Detector Packaging Peer Review September 18, 2012

  45. Engineering Model Cost

  46. Questions?

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